These ongoing studies are directed toward understanding the mechanism by which potassium is secreted into the colonic lumen of mammals. We have identified that there are both active and passive forces regulating potassium secretion in the rat colon. Potassium adaptation that occurs associated with aldosterone adminisration, potassium loading and dexamethasone administration involves alteration of active potassium secretion and is associated with an increase in Na-K-ATPase activity. In addition our studies have domonstrated that glucocorticoid receptors are present in the cytosol of the colonic mucosa and basal colonic electrolyte transport is regulated by glucocorticoid and possibly not by aldosterone.